Optical codes are patterns made up of image areas having different light reflective or light emissive properties, which are typically assembled in accordance with a priori rules. The term "bar code" is sometimes used to describe certain kinds of optical codes. The optical properties and patterns of optical codes are selected to distinguish them in appearance from the background environments in which they are used. Devices for identifying or extracting data from optical codes are sometimes referred to as "optical code readers" of which bar code scanners are one type. Optical code readers are used in both fixed or portable installations in many diverse environments such as in stores for checkout services, in manufacturing locations for work flow and inventory control and in transport vehicles for tracking package handling. Optical code readers have been widely adopted in the routing and sorting of mail.
Most conventional optical scanning systems are designed to read one-dimensional bar code symbols. The bar code is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light reflecting characteristics. One example of a one dimensional bar code is the UPC/EAN code used to identify, for example, product inventory.
The present disclosure relates to techniques especially adapted for reading postal codes. Typically postal codes are characterized by a sequence of bars of uniform width and uniformly spaced along a principal axis of the code. The symbology typically includes a region of regular parallel bars called a clock track. Certain of the bars may extend above and/or below the clock track. These elongated bars are sometimes called ascenders and descenders, and contain coded information.
An example of a postal code is the Postal Numeric Encoding Technique (POSTNET). POSTNET was developed by the U.S. Postal Service to provide an optimized code system for encoding address information on mail. Referring to FIG. 1, the basic elements of the POSTNET code 12 are tall bars or ascenders such as bar 1 and short bars such as bar 2. These bars represent two states, i.e., binary ones and zeros, respectively. Both types of bars are aligned at one edge represented by the line 18 (line 18 is not part of the code symbol). Five bars of code represent one character, for example, one digit of a zip code. The left and right margins of the code are marked by tall bars 3. The postal code called PLANET has a similar structure, but different encoding. In POSTNET code the five bars representing one character include two long and three short bars. In PLANET code the five bars representing one character include three long and two short bars.
Another type of postal code is Canadian Post Office Code. An example of a Canadian Post Office Code is shown in FIG. 1(a). The code is a modified form of the POSTNET code. It is a four-state code with increased alphabetic coding capacity over the POSTNET code described above. The four-states are each exemplified by the ascender bar 4, descender bar 5, full bar 6 (i.e. a bar having both ascending and descending portions) and short, clock bar 7. The clock track lies between lines 8 and 9. (Lines 8 and 9 are not part of the code symbol). Another type of postal code is UK postal code. UK postal code is similar to a two-layer U.S. code with the bottom symbol flipped and the two clock tracks merged. UK code uses 4 bars per character, as compared to 5 bars per character in U.S. POSTNET code. Other four state codes include Australian, Japanese and Belgian Postal Codes.
Postal codes can be read employing imaging devices. For example an image sensor may be employed which has a two dimensional array of cells or photo sensors which correspond to image elements or pixels in a field of view of the device. Such an image sensor may be a two dimensional or area solid state sensor and associated circuits for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view. An imaging module useable in reading postal codes is disclosed in U.S. patent application Ser. No. 09/096,578, filed Jun. 12, 1998, entitled IMAGING ENGINE AND METHOD FOR CODE READERS to Correa et al., which is hereby incorporated by reference. Alternatively, the post processing part of the following algorithm is applicable to systems which use laser scanning imaging, such as the ones disclosed in U.S. patent application Ser. No. 08/275,515 filed Jul. 15, 1994 entitled "Method And Apparatus For Raster Scanning Of Images" to Dvorkis et al., which is incorporated herein by reference.
It is an object of the present invention to provide efficient and accurate techniques for reading postal codes.
It is another object of the present invention to provide techniques for reading postal codes employing an optical imaging system.
It is another object of the present invention to provide techniques for employing an optical imager capable of reading various types of one and two dimensional codes and for identifying and reading various types of postal codes.
It is another object of the present invention to provide techniques for reading postal codes of initially unknown type and orientation with respect to the optical code reader.
These and other objects and features of the invention will be apparent from this written description and drawings.